The expert told LiveScience that people who have survived cardiac arrest later accurately described what was happening around them after their hearts stopped beating.

He said: "They'll describe watching doctors and nurses working, they'll describe having awareness of full conversations, of visual things that were going on, that would otherwise not be known to them."

Explaining when a patient is officially declared dead, he said: "It's all based on the moment when the heart stops.

"Technically speaking, that's how you get the time of death."

His study is examining what happens to the brain after a person goes into cardiac arrest - and whether consciousness continues after death and for how long - to improve the quality of resuscitation and prevent brain injuries while restarting the heart.

Unlike the plot in Flatliners, however, when a person is resuscitated they don't return with a "magical enhancement" of their memories, said Dr Parnia.